Grinding machine



Feb. 16, 1960 Filed May 2?, 1958 J. KLAR ET AL GRINDING MACHINE u .1"Hi1- 3 Sheets-Sheet 1 5 maryn .t. Kunr'holm H 'rney Feb. 16, 1960 J.KLAR ErAL GRINDING MACHINE Filed May 27, 1958' 3 Sheets-Sheet 2INVENTORS John ft'lar By martm Lkumholm H Tney Feb. 16, 1960 J. KLAR HAL3 GRINDING. MACHINE Filed May 2'7, 1958 i 3 Sheets-Sheet 3 I Lfi QQQ '1',0; ma az 34 W- OID. FEED MOTOR MOTOR INVENTORS John ffla r BYWZarlIn .Lffuniholm o neg United States Patent GRINDING MACHINE John Klar, WestBoylston, and Martin L. Kuniholm,

Worcester, Mass., assignors to Heald Machine Company, Worcester, Mass.,a corporation of Delaware Application May 27, 1958, Serial No. 738,13711 Claims. (Cl. 51-88) This invention relates to a grinding machine, andmore particularly to automatic grinding machines having means forcontrolling the feed rate thereof.

fInternal grinding machines employ various methods for holding theworkpieces. The workpiece may be chucked or, in the simplest type ofgrinder, it may be supported between rollers or on shoe-type supports.The object is to support the work while it rotates about a fixed center7 shoes or rolls. If, then,external and internal grinding be carried onsimultaneously, the internal operation need notcomplicate the externaloperation, but it is obvious that the external operation does affect theinternal operation; this is because of the fact that, if the workpieceis supported on rolls or shoes, this causes a change in the position ofthe work center-line and, therefore, complicates the problem of holdingsize on the internal surface.

The problem is resolved if means be provided for guaranteeing that thework center line arrive at a constant position in relation to the worksupports at the same time or before the internal abrading means arrivesat its sizeholding position. The problem is complicated, however, whenthe grinding stock allowance fluctuates, as it normally does, resultingin' a variation in the rate of stock removal due to the resultantvariations in spindle work and machine deflections which, in turn, arecaused by the abrading means becoming dull or glazed to difiering,degrees.

One type of grinding feed mechanism that is well known operates to bringthe wheel and work into engagement and then to maintain a definitepre-set force between the wheel and the work. The cycle time is avariable which is dependent on the magnitude of this force, the amountof grinding stock, the speed of and condition of the abrading member,work speed, etc. An alternate feed method, also wellknown,-consis ts incausing the wheel relatively to approach the work at a present rate.This method results in a cycle time which remains constant but must belonger than the average time of the first method. Thisis because of thefact that the retracted position of the feed member must besuflicientlyfar from the finish position to accommodate a workpiece with the maximumgrinding stock and thefactthat the feed rate cannot be set faster thanthe rate at which the abrading means and machine are able toremovestock. Hence, time is inevitablywasted on all workpieces'withless thanthe maximum stock allowance. Now, in a'combination automatic grinderwhere outer and inner surfaces are ground simul- 2,924,913 Patented Feb.16, 1960 taneously, it has been pointed out that a necessary conditionto successful operation is that the internal and external feed be sosynchronized that, irrespective of initial stock conditions, the arrivalof the outer surface at a given sizeeither earlierthan or co-incidentalwith the arrival of the internal abrading means at its reference pointis necessary in order to hold a uniform internal size. This requirementmakes it necessary to use feeds having constant rate so that both rates,internal and external, can be preset to arrive at the size holdingreference point simultaneously or in any desired relationship,continuously and repetitively. The disadvantage of this method has beenshown to be a wastage oftime on workpieces with less than the maximumpossible stock-but the present invention combines the advantages of thelatter method with those ofthe former method by eliminating the timewasting feature of the latter methods.v The system of. control embodiedin this invention is particularly well adapted to cope with the aboveproblem and offers an easy solutionswhether the machine feed actuatorbehydraulic, electrical or mechanical. The difiiculties presented by theprior arthave been obviated in a manner by the present invention.

It is, therefore, an outstanding object ofthe invention to provide animproved means for controlling feed rates in a grinding machine as afunction of the power absorbed by the grinding wheel or wheels.

Another object of this invention is the provision of a means in agrinding machine whereby the machine is able to sense the amount. ofgrinding stock to be removed from each workpiece. a

It is a further object of this invention to provide a grinding machinehavingmeans for governing the feed in accordance withworkpiece stockallowance thus shortening the time cycle on every workpiece having lessthan however unequally the grinding stock may be distributed betweenouter and inner surfaces and however many] times the feeds are haltedand started as a consequence of maintaining the preset horsepower level,the arrivals of both inner and 'outer abrading surfaces at theirterminal points relative to the workpiece center line will be 00-incidental. i

Another object of this invention is to provide a grinding machine havingan electrical horsepower level control system of simple design withinherent dependability and v long life expectancy.

Although the novel features which are believed to be j characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the invention itself as to its ob ects and advantages, the modeof its operation and the manner of its organizatiom'may be better.understood by referring to the following description,

taken in connection with the accompanying drawings forming a partthereof, and in which: t

Figure 1 is a front eleyational view of a grinding principles of thepresent. inventionz 3 chine embodying the Figure 2 is a plan view of themachine;-' anddrive apparatusdncorporated in Figure 3 is a schematicviewfof certain aeanca iina} the machine.

Referring first to Fig'urejs land 2, .jwherein' arebe st; I I d dthe'grinding machine, indicated generallyby the referencewnume ral 10,1s shown as being of the typeshowiiand describef shown the generalfeatureso'f the invention,

novel the feeds are so controlled that,

in the co-pending patent application of William D. Schmidt and AlmonTownsend, Serial Number 445,152. A base 11 has mounted at one end aworkhead 12 driven by a motor 13. Mounted on the base l l for movementparallehto the axis" of the wheelhead' isa table 14 onwhichis mounted awheelhead l'driven by a motor 16. Adrive piston 17 is associated withthe wheelheadlZ and' a work support -18 of the" shoetype extendsupwardly from the base '11, to supportaworkpiece 19 which; for thepurposes of -descriptiomis shown as being an inner race of a bearing. Aninternal abrasive wheel- 21- is associated 'whh the-wheelhead 15.- Alsomounted on the-base 11 is a secondary-table 22 mounted forpivotaladjustment and carrying an exte'rnah'wheielhead 23 driven by-a motor24'andadapted to'carry an external abrasive wheel-25.' A suitablewheehdres'sing apparatus 26 is mounted- 'on' the'hase 'and isprovided'with a 'di'amond 27 "adapted to dress the' external wheel'25and ai -diamond 28{adaptedito dress the internal 'wheel 21'.

A feed mechanism 29 feeds the=internal grinding Wheel 21 relatively tothe work andis driven through a mag-.

netic clutch 31 (see F-igtir'eii') by afrnotor-=32'. A feedmechar'iism33 feeds the external grinding wheel 25-rela-' tive to: the work and: is:driven' through a magnetic'clutch 34. by amotor 35. The machine isotherwise -as-described in' the above-mentioned. patentapplication ofSchmidt and Townsendx I Referringynow'toFigure 3, power lines 36, 37,and

38areiconnec'ted-to a source of 3-phase electrical power;

not. shown, and are :connected throughfuses 39, '41, and

42 to leads 43, 44,;and 45.2:These leads. are connected through, startercontactors46, 47, .andt48' toleads 49, 5-1, and, 52' connected. to theinternalfdiameter. wheel motor24. The leads 43,44, and'45 arealso'connected respectively through starter contactors53, 54, and 55' toleads 56, 57', and 58 connected togthe outside diameter wheel motor 24.r

Connected in the' lead 52 is the primary 59 of a current transformer 61,having a secondary coil 62; The ends of the secondary coil 62. areconnected to opposite sides of a rectifier 63, one of the leads havinginserted: therein an A.C. ammeter 64; The outputside of the rectifier 63is connected to'leads 65, and 6 6 across-which is connected theresistance element 67 -.of a rheostat 68. The contact arm 69 of-therheostart is connected back to the line 65. The line 65 isalso-connected to-one. end of the' resistance element 71 of a variableresistor-72, the contact arm 73 thereof being connected to one side :ofthe coil 74 of a normally-open sensitive relay-75; One side of theswitch element 76 of the relay75 is connected'toa 0 line 77 by means ofa lead 78.

Inserted in the lead 58 associated with the motor 24 is the primary coil79ofa current transformer 81. The

secondarycoil 82 is connected by leads to the input sides nected to thelead 85. The switch elements 96- are-con nect'ed] across the switchelement 76 associated with the relay. 75, so that one of. the: leadsfrom the switch element 96, isconnected by the lead 78 to the line 77.The other sides of the switch elements 76'and 96, are connected througha lead 97 to one side of the coil 98 forming' part of a normally-closedrelay 99.- The other side oi the coil 98 is'connected by a, lead v101to.a line 102. Theline's 77 andf102 are connected to opposite-polaritiesof, a source of direct current electricity, not-shown; the

polarity. is, of course, immaterial to the"operation. of the apparatus.'Ac'rossvthe coil 98 is connected a resistor; 103 in iseries with; acapacitor 104. One side of the cu d.

contactor 105 associated with the relay 99 is connected to" the'line77byalead'107. Theot'her sideof't'h'e contactor 105 is connected to thecoil 108 of the magnetic clutch 31. The actuating coil 109 associatedwith the magnetic clutch 34 is also connected to the same side of thecontactor 105 as is the coil 108. The other sides of the coils 108 and109 are connected to the line 102. a The line 77 is connected by a lead111 to one side of the rotor of the outside diameter feed motor 35. Theline 77 is also connected by-a lead'112 -to one side of the internaldiameter feed motor 32. The other sides of each of these motors areconnected together and through a lead 113 to the line 102. The fieldcoil 114 associated with the motor 32 is connected on one end to theline 77 and on theother end to a variable resistor 115, the contact armof which is connected through the lead 113 to the line 102. In the samemanner, one end of the-field coil 115 associated wi h, the outside.diameter feed motor 35 "is connected tome, lead V 111' Le 'nnect'ingit"to' the line 77'. The otherfsidefof the fi fcldcoil 1 16'- isconnected toone side of a' Lvar'iable resistorlll f, the contact arm ofwhich is connected throughtlielead' 113, m H6102; l v.

"The operation of the apparatus will now be readily understood invi'ew'of, the'above description." The pawer drawn by the internaldiameterfwheelfm'otor. 1'6'is cated to thecurrent' transformerbyfthepassage of one phase'of the current throughthe primary coil 59thereof.

The voltage appears acrossthe output coil '62 which is 'pro v portionaltothe currentinftheleafd 152 and therefore ap'-.

proximately. indicative" of nertia d awn, by the motor; The outputsignal of thecur'rent transformer 61 is alter nating "but, aftertreatment by the rectifier 63, emerges as a series of'directcurrentjp'ulsesjofa iriagnitu'deindicative of the power drawn by thernotori' Therelay is so constructed that; whenthe'size'of the p lScsrea'ching it is great enough, theswi'tch "element76jwill close.

Inthe same way, the current drawn by the motor 24iis,

felt by the primary coil' 79' of thecurrent' transformer 81. Analternating voltage appears on thc output leads of the coil 82indicative of the power drawn by t he" motor 24. This alternating signalis rectified 'by the rectifier 83 and is impressedon the coil 94 of therelay" 95. When agiven pulseis large enough, the switch 96 closes; Theclosure ofeithen'or both of the switch elements 76 and .96causes a flowof current through the coil 98 of the relay-91am current'pa'sses fromthe line 77 through the lead 78; through one ofythe two switches76-and96, andthroughthelead97, the coil 98 and'the lead 101 to the line102. A similar; current' passes through the resistor 103 and thecapacitor 104. A sumcientflow of current through the coil 98*causes anope' n ingof the contactor 105' thus cutting off the flow of" current tothe coils 108' and 109 associated with the clutches 31 and 34respectively. As is evident from "a study of Figure' -3, themotors 32and 35* operate continuously but the deactivation of the clutches-"108and 109 causes "the cutting-off-pf power transmittal fromf these motorsto the feed me'chanisms 29 and'33. It will f be understood that therelays 75-and are very-sensitive.

The variable resistance 68 acts as a means of adjustingthe 1 sensitivityof thereby 75 anda variable '-res'istancc SSperformsa similar functionin 'conne'ction with ftli'c 4 relay 95. An additionalfadjustrrientofsensitivity'isprovided' by the variable resistance's '72 and 92;-'=Suppose that the control he setat= 3 hp; 'As the wheel feedsinto' thework the'powerloading increases fromit's freerunning. value towards the3 hp. valuje. Th'e'contact carryingarmature of thesensitiverelayaorsolenoid-actaf ated switch 75 is subjectto. two opposingiforces;there'lay" spring tries. to maintaimtherelay: contact open while thepulsing at twice the supply current frequency, and only the differencebetweenthe magnetic force and the spring force is available to effectclosure. If this switch element be used to control the feed through anon-oif device such as a magnetic clutch, a rapid functioning'results.This becomes especially true if two clutches (as for an internal feedand external feed, such as we have in the present case) be operated fromone ordinary sensitive relay. At the threshold of operation the switchelement 76 (and the switch element 96, for that matter) behaves like afaulty rheostat with a large voltage drop across the contact. This, inturn, results in feeding of the clutch which operates at the slightlylower energy level, while the other clutch fails to drive. Thissituation could not be tolerated on a machine for simultaneouslygrinding outer and inner surfaces for the previously-described reasonthat a necessary condition of the operation of such a machine isaccurate synchronization of the internal and external feeds. To avoidthis difliculty the operation of the sensitive relay is converted froman erratic to a positive action by providing the relay 99 which isshunted by an integrating capacitor 104 and resistor 103. The functionof the integrating capacitor is to accumulate the pulse energy deliveredby the switch elements 76 and 96 and, when the energy level reaches thatrequired by the resistor 103 and the relay 99, it causes a sustained(unpulsed) actuation of the relay 99. The positive action on the relay99 efficiently and cleanly interrupts both feeds, whereupon the powerloading of the spindle motors diminishes until the switch elements 76and 96 are both open. The energy accumulated in the capacitor 104dissipates meanwhile through the resistor 103 and the coil 98 of therelay 99 until it reaches the level where release of the contactor 105occurs. The contactor then closes with a positive action and theenergization of the coils 108 and 109 and the operation of the feedmechanisms 29 and 33, respectively, are again actuated.

The power differential between pull-in and dropout of the relay 99 isrelated to the values of the capacitor 104 and the resistor 103 whichare in parallel with the relay, and related as well as to the internalresistance of the relay itself. These elements can be so chosen that thefeed advances by small or large increments, each type of performancehaving its own advantages in specific cases. In the preferred embodimenta relay 99 is used having a high internal resistance and a resistance isplaced in series with the capacitor to reduce the .current flowingthrough the sensitive relays 75 and 95. The switch element 76 and 96,because of the low pressure vibratory.

type of operation (with consequent arching) would not otherwise have along nor dependable life expectancy. In a specific example the relays 75and 95 have an internal resistance of one ohm, the resistor 103, aresistance of 10,000 ohms, the capactor 104, a capacity of 4microfarads, and the relay 99 an internal resistance of 10,000 ohms.Suppose that it is desired to set up the grinding machine tosimultaneously grind the outer and inner surfaces of a ring where themaximum stock found on the outer surface is .030" on the diameter and.025" on the inner diameter. Suppose further that it is possible toremove .028 from the outer surface in 28 seconds and .026" on the innersurface in 26 seconds, these rates being close to, but safely under'thecritical point where the abrading surface might be severely crushed ordamaged. This would allow .002 for further finishing of each surface.Instead of setting the rates on internal and external feeds to a 28thsecond cycle (the slower of the two) the present invention makes itpossible to set the feed rates of each at a much faster rate, say, 4times faster or 7 seconds. At the same time the danger of exceeding thecritical wheel pressure is overcome by setting the external and internalpower load adjustments to values which are consistent with that facevalue producedby the 28 second cycle on the outer surface and 26 secondcycle onthe internal surface. A

comparison can now be made between the time taken by two machines, oneequipped with this invention and one without. The average grinding stockwill be assumed to be .014" on the outer surface and .013" on the innersurface. Without this power control the cycle time would be an unvarying28 seconds. With this control the 7 seconds pre-set rate wouldaccomplish the first .014" of feed (where no stock is encountered) inone half the 7 seconds or 3 /2 seconds. The second half of the feedwould require 14 seconds. The total average time with the use of thisinvention would be 14 plus 3% or 17% seconds, compared to the 28 secondsfor the machine without it. This is a large saving in time and themachine is rendered 60% more productive in rough grinding.

While certain novel features of the invention have been shown anddescribed and are pointed out in the annexed claims, it will beunderstood that various omissions, substitutions,and changes in theforms and details of the device illustrated and in its operation may bemade by those skilled in the art without departing from the spirit ofthe invention.

The invention having been thus described what is claimed as new anddesired to secure by Letters Patent is:

1. A grinding machine, comprising an internal grinding wheel, aninternal wheel motor, an external grinding wheel, an external wheelmotor, an internal feed mechanism, an external feed mechanism, a firstmeans for driving the internal feed mechanism, a second means fordriving the external feed mechanism, and means operative when the powerconsumed by either motor exceeds a predetermined value to render boththe first and the second means inoperative.

2. A grinding machine, comprising an internal grinding wheel, aninternal wheel motor, an external grinding wheel, an external wheelmotor, an internal feed mechanism, an external feed mechanism, a firstmeans for driving the internal feed mechanism, a second means fordriving the external feed mechanism, a third means giving a signalproportional to the power consumed by the internal wheel motor, a fourthmeansgiving a signal proportional 1 to the power consumed by theexternal wheel motor, and means operative when the signals from eitherthe third or the fourth means exceeds a predetermined value to renderboth the first and the second means inoperative.

3. A grinding machine for use in simultaneously abrading external andinternal surfaces of a workpiece, comprising an internal grinding wheel,internal wheel motor, and external grinding wheel, an external wheelmotor, an internal feed mechanism, an external feed mechanism, a firstmotor for driving the internal feed mechanism, a second motor fordriving the external feed mechanism, a first means giving a signalproportional to the power consumed by the external wheel motor, and arelay operative when the signal from either first or the second meansexceeds a predetermined value to render both the first and second motorsinoperative.

4. A grinding machine, comprising an internal grinding wheel, aninternal wheel motor, an external grinding wheel, an external wheelmotor, an internal feed mechanism, an external feed mechanism, a firstmeans including a motor and clutch for driving the internal feedmechanism, a second means including a motor and clutch for driving theexternal feed mechanism, a third means giving the signal proportional tothe power consumed by the internal wheel motor, a fourth means giving asignal proportional to the power consumed by the external wheel motor,and means operative when the signals from either the third or the fourthmeans exceed a predetermined value to render both clutches associated,with the first and second means inoperative.

5. A grinding machine for use in simultaneously abrading external andinternal surfaces of a workpiece, comprisinganinternal grinding wheel,an internal wheel motor, an external grinding wheel, an external wheelmotor, an internal feed' "rne chanism, an external feed mechanism, afirst means for driving the internal feed mechanism, a second means fordriving the external feed mechanism, a third means giving a signalproportional to the power consumed by the internal wheel motor, a firstrelay operated when the signal from the third means exceeds apredetermined value, a fourth means giving a signal proportional to thepower consumed by the external wheel motor, a second relay operated'whenthe signal from the fourth means exceeds a predetermined value, and athird relay actuated by the operation by. either the first or the secondrelay to render both the first and second means inoperative to drivetheir? respec: tive feed mechanisms.

6. A grinding machine for use, in simultaneously abrading external andinternal surfaces of a workpiececomprising an internal grinding wheel,an internal: wheel motor, an external grinding wheel, an external wheelmotor, an internal feed mechanism, aneexternal feed mechanism, a firstmeans including a motor; and. clutch for driving the internal feedmechanism, a second means including a motor and clutch for driving theexternal feed mechanism, the third means giving a signal proportional tothe power consumed by the internal; wheel motor, a first relay operatedwhen the signal from the third means exceeds a predetermined value, avfourth means giving a signal proportional to the powercon sumed by theexternal wheel motorya second relay operated when the signal from thefourth means, exceeds av predetermined value, and a third relay actuatedby the operation by'either the first or the secondrelay to render boththe clutches of the first and second means inoperative to connect theirrespective motors totheir respective feed mechanisms.

7. A grinding machine for use in simultaneously abrading external andinternal surfaces of a workpiece,'com-. prising an internal grindingwheel, an internal wheel motor, an external grinding wheel, an externalwheel motor, an internal feed mechanism, an external feed mechanism, afirst means including amotor and clutch for driving the internal feedmechanism, a second means.

including the motor and clutch for drivin glthe external feed mechanism,a first current transformer connected in a lead to the internal wheelmotor giving asignal protion of either the first or second relay torender both clutches of the first and second means inoperative toconnect their respective motors to their respective feed mechanisms.

8. A grinding machine for use. in simultaneously abrading' external andinternalsurfaces of a workpiece, an internal grinding wheel, an internalwheel motor. of the alternating current type, an external grindingwheel, an external wheel motor of the alternating:

current type, an internal feed mechanism, an external feed mechanism, afirst means including a=motor and clutchfor driving theinternal feedmechanism, a second means including a motor and clutch for drivingthefexternal feed mechanism, a third. means giving a signal proportionalto the power consumed-by the. internal wheel motor, a first .'sensitiverelay, operated whenfthesigrial from the third means exceeds. a.predetermined value, a fourth meansjgivinga signal'prop'or tionalto thepower consumed'by the external wheel motor, a second sensitive relayoperated when the signal from the fourth means'jexceedsapredetermined-value,"

a third relay actuatedby' th'e 'operation of eithith first. or thesecond relay to render both clutches of the are; and second means:inoperative to connect their respective motors to their! respective feedmechanisms, and a capacitor connected across the third relay torender'it insensitive to. high frequency opening and closing of thefirst and second relays.

9. A grinding machine for use in simultaneously abrading internal andexternal surfaces of a workpiece, comprising an internal grinding wheel,an internal wheel motor of the alternating current type, an externalgrinding wheel, an external; wheel motor of the alternating currenttype, an internal feed mechanism, an external feed mechanism, a firstmeans including a motor and clutch for driving the internal feedmechanism, a second means including a motor and clutch for driving theexternal feed mechanism, a first current transformer connected in alead. totheinternal wheel motor giving a signal proportional to thepowerconsumed thereby, a first sensitive relay operated when the signalfrom the first'current transformer exceeds a predetermined value, a.second currenttransformer connectedin a lead to the external wheel motorgiving a signal proportional to the power consumed thereby, asecondsensitive relay operated when the signal from the second currenttransformer exceeds. a predetermined value, a third relay actuated bythe operation of either the first or second relay to render bothclutches of the first and second means inoperative to connect theirrespective motors to their respective feed mechanisms, anda capacitorconnected across the coil of the third relay to render it insensitive tohigh frequency opening-and closing of the first and second relays. I

10. A grinding machine, comprising a grinding wheel, a wheel motor ofthe alternatingcurrent type, a feed mechanism, a first means for drivingthe feed mechanism, a second means giving a signal proportional to thepower consumed by'the wheel motor, a sensitive relayoperated when thesignal from the second means exceeds a predetermined value, a secondrelay actuated by the operation of the sensitive relay to render thefirst means inoperative to drive the feed mechanism, and a capacitorconnected across the coil of the second relay to render it insensitiveto high frequency opening and closing of the first and second relays.

11. A grinding machine for use in simultaneously finishing external andinternal surfaces of revolution of a workpiece, comprising aninternalgrinding wheel, an internal wheel motor for carrying on the finishingoperation on the internal surface, an external grinding wheel, anexternal wheel motor for carrying on the finishing operation on theexternal surface, an internal feed mechanism, an external feedmechanism, the feed mechanisms being arranged to bring the internal andexternal finishing operations to a conclusion at approximately the sametime, a first means for driving the internal feed mechanism, a secondmeans for driving the external feed mechanism, a third means giving asignal proportional to the power consumed by the internal wheel motor incarrying on thefinishing operation of the internal surface, a fourthmeans giving a signal proportional to the power consumed by the externalwheel motor in carrying on the finishing operation on'the externalsurface, the feed ratesbeing substantially greater than the rate whichwill maintain the power consumed by the wheel motors below the saidpredetermined values during the finishing cycle, the predeterminedvalues being those above which operation is destructive of the wheel,and means operative when the signals from either the third or the fourthmeans. exceedfa predetermined. value to render both the f l $995 5 t tte i i i l a a Refg -ence Cited in the file of this patent UNITEDfSTATESPATENTS 2,694,883 ,Balsiger Nov. 23, 1954 2,807,916 Squire Oct. 1 1957

